Optical module and its wavelength monitor control method

ABSTRACT

The present invention provides wavelength monitoring and/or control enabling size reduction and low power operation without requiring a complicated optical system in its wavelength monitoring and controlling mechanism.  
     The measurement portion ( 1 ) measures temperature by a thermistor ( 5 ) in the measurement portion, and measures a bias current by using an LD drive current detecting circuit ( 6 ). The LD temperature, optical output and bias current are measured by the measurement portion. The relationship between the LD temperature and wavelengths or between the temperature, bias current and wavelengths is stored in a memory map of the storage portion ( 2 ). The central controlling portion ( 3 ) calculates wavelengths on the basis of the temperature and the bias current or the temperature information of the measurement portion, and the relationship between the LD temperature, bias current and wavelengths or between the temperature and wavelengths of the storage portion.

TECHNICAL FIELD

The present invention relates to an optical module, a wavelengthmonitoring method, and a wavelength monitoring and controlling methodthereof. In further detail, the invention relates to a wavelengthmonitoring method in an optical transmitter module and an opticaltransmitter and receiver module, a wavelength controlling method and awavelength monitoring and control method in an optical transmittermodule and an optical transmitter and receiver module.

BACKGROUND ART

In recent years, an increase in the transmission capacity of atransmission line has been demanded in line with an increase in Internettraffic. To meet this demand, a wavelength division multiplexingtechnology (WDM) which is capable of transmitting data with differentwavelengths bundled by a single core fiber has been introduced centeringon the core network. Herein, where the WDM technology is employed, anoptical coupling and splitting filter having a satisfactory wavelengthselection property is needed since different wavelengths transmitrespectively individual types of information.

In addition, since crosstalk between signals of different wavelengthsbecomes a factor of signal deterioration, it is necessary that thewavelength of a laser diode (LD) which is used as a signal source isstabilized in a passband of an optical coupling and splitting filter. Inparticular, in a Dense WDM (DWDM) technology having high density, sincethe pass band of the optical coupling and splitting filter is narrow, itis necessary to carry out wavelength monitoring and control.

Since the accuracy of monitoring and controlling the wavelength dependson an interval between wavelengths, the accuracy in wavelengths is madesevere in line with narrowing of the interval between wavelengths. Forexample, in the DWDM technology used for the core network, the intervalbetween wavelengths is mainly 200 GHz through 50 GHz (1.6 nm through 0.4nm). In the near future, the interval will be made narrower still.

An oscillating wavelength of the LD is greatly influenced bytemperature. Usually, a wavelength monitoring and controlling mechanismis provided in the interior of an optical transmitter module or anoptical transmitter and receiver module. The wavelength monitoring andcontrolling mechanism feeds monitor output signals for monitoring andcontrolling wavelengths back to a temperature controller and carries outcontrol so that the oscillating wavelengths are kept constant.

FIG. 12 is a general view of a prior art wavelength monitoring andcontrolling mechanism disclosed in, for example, “25 GHz-spacingwavelength monitor integrated DFB laser module” of Institute ofElectronics, Information and Communication Engineers C-4-44, 2002, whichwas prepared by Takagi et.al., and the schematic shows one example of anoptical system for monitoring and controlling wavelengths in which anetalon (or Fabry-Petrot optical resonator) is employed. In the drawing,reference number 12 denotes an optical fiber, 13 denotes a forward lens,14 denotes a DFB-LD (a distributed feedback laser diode), 15 denotes arearward lens, 16 denotes a prism, 17 denotes a temperature controller,18 denotes an etalon, 19 a and 19 b denote optical detectors. Awavelength monitoring and controlling method using an etalon in anoptical system for monitoring and controlling wavelengths is alsodisclosed in Japanese Patent Application Laid-open Nos. 2001-196689 and2003-283044, and U.S. Pat. No. 6,353,623.

The DFB-LD 14 is installed centrally, and an optical transmission systemfor optical signals is shown at the arrow A side. A laser beam emittedfrom the forward end face is collimated by the forward lens 13 and iscoupled into an optical fiber 12. On the other hand, an optical systemfor monitoring and controlling wavelengths of the DFB-LD 14 is shown atthe side opposite to the arrow A. An LD beam emitted from the rearwardend face is used for monitoring and controlling. The LD beam iscollimated by the rearward lens 15 and is branched into two by the prism16. One of the split LD beams is coupled directly to the opticaldetector 19 a and the other thereof is made incident into the etalon 18.Output signal of the light made incident directly into the opticaldetector 19 a are used for automatic optical output control.

Output signals made incident into two optical detectors 19 a and 19 bare used for monitoring and controlling wavelengths. Light passedthrough the etalon 18 is collimated and is made incident into theoptical detector 19 b. The resonator length of the etalon 18 isaccurately adjusted so as to correspond to a wavelength to be monitored.Therefore, since the amount of outputted light changes in line with afluctuation in the wavelength, a difference between the light amount andthe output signal made incident into optical detector 19 a is detectedas a fluctuation in output of the optical detector 19 b. The output isfed back to the temperature controller 17 of the LD light, therebycontrolling the wavelength of the LD light. Thus, the wavelength isdirectly extracted in terms of hardware and is used for control.

On the other hand, a method for monitoring and controlling wavelengths,in which no etalon is employed for an optical system for monitoring andcontrolling wavelengths, has been developed. For example, in JapanesePatent Application Laid-open No. 1-235390(1989), a method for monitoringand controlling a wavelength, in which the relationship between anenvironmental temperature and a change in a wavelength (that is, anamount of wavelength deviation) is stored in advance and the temperatureis controlled based on the relationship, is disclosed. In JapanesePatent Application Laid-open No. 2000-323785, a method for monitoringand controlling a wavelength, which stores in advance the data obtainedby actually having measured the laser temperature with respect to thelaser drive current and controls a laser drive current by predicting anactual amount of rise in temperature on the basis of the data, isdisclosed as another example.

As described above, in order to suppress crosstalk which becomes afactor of signal deterioration, wavelength monitoring and controllingare indispensably necessary to stabilize the oscillating wavelength of alight source within the pass band of an optical coupling and splittingfilter. However, where an optical filter such as an etalon is employedfor a wavelength monitoring and controlling system, the optical systembecomes expensive, and the number of assembling steps is increased,making it difficult to reduce the production costs. Also, since theetalon has temperature dependency (for example, Y. C. Chung et. al,“Synchronized etalon filters for standardizing WDM transmitter laserwavelength,” IEEE Photon. Technol. Lett., Vol., pp. 186-189, February1993), for example, a Peltier device is requisite. As a result, it isdifficult to make the wavelength monitoring and controlling system smallin size. In addition, there is still another problem in that, since thetemperature adjusting feature operates at all times to secure areference temperature, power consumption for adjusting the temperaturebecomes high.

On the other hand, in the method for monitoring and controlling awavelength, which does not employ an etalon filter in a prior artoptical system for monitoring and controlling a wavelength, for example,in the cases of Japanese Patent Application Laid-open Nos.1-235390(1989) and 2000-323785, the temperature is controlled using therelationship between the environmental temperature stored in advance anda change in the wavelengths (that is, an amount of wavelength deviation)without directly calculating the wavelength. Therefore, where a changein the wavelength (that is, an amount of the wavelength deviation)depends on factors other than the temperature, sufficient monitoring andcontrol cannot be secured.

DISCLOSURE OF THE INVENTION

The present invention was developed in order to solve such problems andshortcomings. It is therefore an object of the invention to provide anoptical module and its wavelength monitoring and controlling method,enabling small size and low power consumption without requiring anycomplicated optical system in its wavelength monitoring and controllingmechanism. Further, it is another object of the invention to provide anoptical module and its wavelength monitoring and controlling methodwhich is capable of controlling a wavelength of light emitted from alaser diode (LD) to a desired value.

The invention was made in order to achieve the above-described objects.According to a first aspect of invention, an optical transmitter moduleor an optical transmitter and receiver module internally comprises: ameasurement portion for measuring the temperature and bias current of alaser diode or only the temperature; a storage portion in which therelationship between the temperature and bias current and wavelengths orbetween only the temperature and wavelengths are stored; and a centralcontrolling portion for controlling the measurement portion and thestorage portion, wherein the wavelength is calculated on the basis ofthe relationship stored in the storage portion.

Also, according to a second aspect of the invention, a wavelengthmonitoring method in an optical transmitter module or an opticaltransmitter and receiver module internally comprising a measurementportion for measuring the temperature and bias current of a laser diodeor only the temperature, a storage portion in which the relationshipbetween the temperature and bias current and wavelengths or between onlythe temperature and wavelengths, and a central controlling portion forcontrolling the measurement portion and the storage portion, the methodcomprises the step of calculating wavelength information on the basis ofthe temperature and bias current or only the temperature measured by themeasurement portion, and the relationship between the laser diodetemperature and bias current and wavelengths or between the laser diodetemperature and wavelengths stored in the storage portion.

Also, according to a third aspect of the invention, a method formonitoring and controlling wavelengths in an optical transmitter moduleor an optical transmitter and receiver module internally comprising ameasurement portion for measuring the temperature and bias current of alaser diode or only the temperature, a storage portion in which therelationship between the temperature and bias current and wavelengths orbetween only the temperature and wavelengths, a central controllingportion for controlling the measurement portion and the storage portion,and a temperature adjusting portion composed of a temperaturecontrolling device, the method comprises a wavelength informationcalculating step of calculating wavelength information on the basis ofthe temperature and bias current or the temperature measured by themeasurement portion, and the relationship between the laser diodetemperature and bias current and wavelengths or between the laser diodetemperature and wavelengths stored in the storage portion, and atemperature controlling step of adjusting the internal temperature byusing the calculated wavelength information to feed back to thetemperature adjusting portion.

Thus, with respect to monitoring wavelengths and monitoring andcontrolling wavelengths by calculating the wavelengths on the basis ofthe relationship between the LD temperature and bias current and thewavelength and between the LD temperature and wavelengths stored inadvance in the storage portion, since the system does not require anycomplicated optical system in which an etalon filter is used as in theprior art, the structure thereof can be simplified, and reduced size andcost can be expected. For example, even in a Coarse WDM (intervalbetween wavelengths is 1000 GHz through 50 nm, ITU-TG. 694.2) which doesnot require wavelength monitoring and control, the use of such awavelength monitoring feature improves reliability in operationmanagement such as enabling a proactive measure against an emergentcondition of a system, thus providing a great effect.

In addition, in terms of the wavelength monitoring and control, byassociating the temperature adjustment feature with an externaltemperature, minimal operation required for the temperature adjustmentfeature can be achieved when the external temperature exceeds theminimum value or the maximum value of the wavelength threshold, wherebythe power consumption can be decreased in comparison with a case wherethe temperature adjustment feature is operated at all times. Further, byusing a temperature control feature, a dense WDM technology can beemployed, making it possible to increase the number of wavelengths per asingle core. Further, by storing, not a deviation from a predeterminedwavelength, but the wavelength itself in a memory, it becomes possibleto set an oscillating wavelength to any value within a variable range ofthe temperature adjusting portion.

As described above, according to the invention, wavelength monitoring isenabled by the measurement portion for measuring the temperature andbias current of a laser diode or only the temperature; the storageportion in which the relationship between the temperature and biascurrent and wavelengths or between only the temperature and wavelengthsis stored; and the central controlling portion for controlling themeasurement portion and storage portion. In addition, wavelength controlis enabled by adding the temperature adjusting portion, which iscomposed of a temperature controlling device, inside the opticaltransmitter module or optical transmitter and receiver module. Thesetechnologies can be applied for size reduction and mass production, andexpected to have a wavelength monitoring and controlling feature to beadded to an optical transmitter module and an optical transmitter andreceiver module.

Also, by associating the temperature adjustment feature with an externaltemperature, minimal operation required for the temperature adjustmentfeature can be achieved when the external temperature exceeds theminimum value or the maximum value of the wavelength threshold, wherebythe power consumption can be decreased in comparison with a case wherethe temperature adjustment feature is operated at all times.

By using a wavelength monitoring method in an optical transmitter moduleor an optical transmitter and receiver module according to theinvention, reliability in operation management can be improved by thewavelength monitoring feature. In addition, by using a wavelengthmonitoring and controlling method in an optical transmitter module or anoptical transmitter and receiver module according to the invention, ahighly dense WDM technology having narrow intervals between wavelengthscan be introduced by the wavelength controlling feature, making itpossible to increase the number of wavelengths per a single core in anoptical system.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an optical module for monitoringwavelengths according to the invention;

FIG. 2A is a table showing the relationship between LD temperature andbias current and wavelengths;

FIG. 2B is a table showing the relationship between the LD temperatureand wavelengths;

FIG. 3 is a flow chart showing a procedure of a wavelength monitoringmethod of an optical module according to the invention;

FIG. 4 is a block diagram of a wavelength monitoring and controllingoptical module according to the invention;

FIG. 5 shows a memory map internally incorporated in SFP;

FIG. 6 is a flow chart to describe a wavelength monitoring procedure ofa wavelength monitoring optical module according to the invention;

FIG. 7 is a graph to describe a wavelength calculating procedureaccording to the invention;

FIG. 8 is a flow chart to describe a wavelength monitoring andcontrolling method of a wavelength monitoring and controlling opticalmodule according to the invention;

FIG. 9 is a flow chart to further simplify the wavelength monitoring andcontrolling procedure of the wavelength monitoring and controllingoptical module according to the invention;

FIG. 10 is a flow chart to describe a wavelength monitoring andcontrolling procedure of the wavelength monitoring and controllingoptical module according to the invention;

FIG. 11 is a flow chart to describe a wavelength monitoring andcontrolling procedure of the wavelength monitoring and controllingoptical module according to the invention; and

FIG. 12 is a schematic of a prior art wavelength monitoring andcontrolling mechanism.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, a description is given of embodiments of the invention withreference to the accompanying drawings.

An optical module according to a first embodiment is described below.FIG. 1 shows a configuration of a wavelength monitoring optical moduleaccording to the first embodiment. In the drawing, reference number 1denotes a measurement portion, 2 denotes a storage portion, 3 denotes acentral controlling portion, 4 denotes a laser diode (LD), 5 denotes athermistor, 6 denotes an LD drive current detecting circuit, 7 denotesan LD drive current controlling circuit, and 8 denotes a photo diode(PD).

The measurement portion 1 measures the temperature by a thermistor 5 inthe measurement portion 1, and measures the bias current by using the LDdrive current detecting circuit 6, and further measures an opticaloutput by the PD 8. In addition, the LD drive current controllingcircuit 7 controls the bias current of the LD 4, and feeds it back viathe central controlling portion 3 on the basis of the information of thebias current calculated by the measurement portion 1.

And, as shown in FIG. 2A and FIG. 2B, wavelengths are calculated by thecentral controlling portion 3 on the basis of the relationship (FIG. 2A)between the LD 4 temperature, bias current and wavelengths, or therelationship (FIG. 2B) between the LD 4 temperature and wavelengths,which are stored in the storage portion 2.

Generally, an oscillating wavelength can be linearly approximated by theLD 4 temperature and bias current. For example, the wavelength can becalculated by a linear interpolation method from the measured values ofthe temperature and bias current, using a data table such as shown inFIG. 2A.λ=λc+aT+b(i−ic)   (1)

where λc is a wavelength at temperature 0° C. and threshold currentvalue ic, a and b are coefficients, T is a temperature, and i is a biascurrent.

For example, if the bias current is 80 mA and the temperature is 27° C,the wavelength becomes 1546.30 nm, wherein a=90 pm/°C. and b=3 pm/mAwere employed. Also, since b is small, the wavelength may be calculatedon the basis of only the relationship between the temperature andwavelength for simplification as shown below.λ=λc+aT   (2)

The wavelength may be calculated by another method described in detaillater.

FIG. 4 is a block diagram of a wavelength monitoring and controllingoptical module according to the invention. In the drawing, referencenumber 9 denotes a temperature adjusting portion, 10 denotes a Peltierdevice, and 11 denotes a Peltier device current controlling circuit. Inaddition, components which have the same function as those in FIG. 1 aregiven the same reference numbers.

Wavelength monitoring and controlling are carried out by the Peltierdevice 10 and Peltier device current controlling circuit 11 in thetemperature adjusting portion 9. Also, it is possible to carry outoptical output control by using the PD 8 and LD drive currentcontrolling circuit 7. That is, the wavelength monitoring andcontrolling optical module shown in FIG. 4 is such that the wavelengthmonitoring optical module shown in FIG. 1 is provided with thetemperature adjusting portion 9 composed of a temperature controllingdevice and is also provided with a feature of feeding wavelengthinformation calculated from the storage portion 2 back to thetemperature adjusting portion 9.

Next, a description is given of a wavelength monitoring method in anoptical transmitter module or optical transmitter and receiver moduleaccording to a second embodiment of the invention. By setting thresholdvalues related to the wavelengths in the storage portion 2 and comparingthe wavelengths calculated by the central controlling portion 3 with thethreshold values, it becomes possible to issue an alarm or a warningwith respect to wavelength deviation.

As a detailed example, a description is given of a Small Form FactorPluggable (SFP) in which an optical portion of a device is formed of apluggable small-type optical transmitter and receiver module. Withrespect to the SFP, the wavelength monitoring method is defined inSFP-8472 Revision 9.3 by the SFP Committee. A memory map held by the SFPis illustrated in FIG. 5.

Herein, threshold values for the alarm and warning are established in anarea of 56 bytes in the Alarm and Warning Thresholds addresses 0 through55 of the storage portion 2. Temperature, optical transmission output,bias current of the LD, optical receiving input, and supply voltage arestored in an area of 24 bytes in the Real Time Diagnostic Interfaceaddresses 95 through 119 of the storage portion 2, and two additionalitems can be stored, whereby all-time monitoring is enabled.

Herein, the LD temperature, bias current and optical output are measuredby the measurement portion 1. Further, bits are assigned in the portion,which are prepared to transmit alarm or warning information to aperipheral interface if the alarm or warning thresholds are exceeded.

However, no wavelength information is included in the SFP. Therefore, itbecomes possible to carry out wavelength monitoring by newly addingwavelength information to the place of the above-described additionalitems. With respect to the method for calculating wavelengthinformation, the relationship between the LD temperature and wavelengthsor between the LD temperature and bias current and wavelengths as shownin FIG. 2A and FIG. 2B are stored in advance from the measured values ofLD (herein, DFB-LD) in a memory area of 120 bytes of the User WritableEEPROM addresses 127 through 247 or an extended memory of the storageportion 2. Further, the relationship between the LD temperature andwavelengths or between the temperature, bias current and wavelengths maynot employ individual measurements but rather use a singlerepresentative value or a designed value although the accuracy issomewhat worsened.

And, a wavelength is calculated by the central controlling portion 3 onthe basis of the temperature and bias current or the temperatureinformation measured by the measurement portion 1 and the relationshipbetween the LD temperature, bias current and wavelengths or between thetemperature and wavelengths stored in the storage portion 2.

In addition, by setting the threshold values for wavelengths in theAlarm and Warning Thresholds of the storage portion 2, it becomespossible to issue an alarm or warning with respect to wavelengthdeviation by the central controlling portion 3.

FIG. 3 is a flow chart showing the procedures of a wavelength monitoringmethod of an optical module according to the invention.

First, the temperature, bias current and optical output are measured bythe measurement portion 1 (S1). Next, by mapping information of themeasurement portion in the Real Time Diagnostic Interface of the storageportion 2 (S2), a wavelength is calculated (S3) by collating only thetemperature information or the temperature and bias current informationwith the matrices in the User Writable EEPROM or extended memoryportion.

Next, the minimum threshold value of a wavelength warning in the Alarmand Warning Thresholds of the storage portion 2 is compared withtransmitted wavelength information (S4). If the transmitted wavelengthinformation is smaller than or equal to the minimum threshold value ofthe wavelength warning, the Wavelength LOW warning bit in the Real TimeDiagnostic Interface of the storage portion 2 is set to 1, and a warningsignal is outputted to a peripheral interface, etc. (S6).

If the transmitted wavelength information exceeds the minimum thresholdvalue of a wavelength warning, then it is compared with the maximumthreshold value of the wavelength warning in the Alarm and WarningThresholds of the storage portion 2 (S5). When the transmittedwavelength information is larger than or equal to the maximum thresholdvalue of a wavelength warning, the Wavelength HIGH warning bit in theReal Time Diagnostic Interface of the storage portion 2 is set to 1, anda warning signal is outputted to a peripheral interface, etc. (S7). Ifit is smaller than or equal to the maximum threshold value of awavelength warning, a status is set, in which no wavelength warningsignal of the Real Time Diagnostic Interface of the storage portion 2 isoutputted (that is, warning bit is 0), and the temperature, bias currentand optical output are again measured by the measurement portion 1.

FIG. 6 is a flow chart showing another embodiment of the wavelengthmonitoring method in an optical transmitter module or opticaltransmitter and receiver module according to the invention. Theembodiment differs from the wavelength monitoring method shown in FIG. 3in terms of the wavelength calculating method (S3). The steps (S1, S2,and S4 through S7) other than S3 in FIG. 6 are the same as those in FIG.3.

In the wavelength calculating method according to the embodiment shownin FIG. 3, coefficients of the equations (1) and (2) are obtained bycollating only the measured temperature information or the temperatureand bias current information with the matrices in the User WritableEEPROM or in the extended memory area. After that, the wavelength iscalculated on the basis of the coefficients (S3). In the wavelengthcalculating method shown in FIG. 6, two temperature values which are asmaller value and a larger value than the measured temperature value,and two bias current values which are a smaller value and a larger valuethan the measured bias current information are selected from thematrices of a user writable EEPROM such as in FIG. 2A, and it ispossible to calculate the wavelength by extracting wavelengths at thefour points corresponding to these values (For example, four pointsnearest to the measured values of the temperature and bias current maybe taken). In detail, it is possible to calculate the wavelengths bymeans of the measured temperature and bias current of the LD 4 and theselected four wavelengths from the relationship between the laser diodetemperature, bias current and wavelengths stored in the storage portion2.

Referring to FIG. 7, a further detailed description is given below.First, a smaller temperature value T1 than the above measuredtemperature Tmes, a larger temperature value T2 than the above measuredtemperature Tmes, a smaller bias current value I1 than the abovemeasured bias current Imes and a larger bias current value I2 than theabove bias current value Imes are selected. And, the corresponding fourwavelengths (λ11=λ(I1, T1), λ21=λ(I2, T1), λ12=λ(I1, T2), and λ22=λ(I2,T2) are extracted. Further, the bias current dependency of thewavelengths at temperature T1 is linearly interpolated by using λ11 andλ21, and the wavelength λmes1=λ(Imes, T1) at Imes is calculated.Similarly, the bias current dependency of the wavelength at temperatureT2 is linearly interpolated by using λ12 and λ22, and the wavelengthλmes2=(Imes, T2) at Imes is calculated. Finally, using the calculatedλmes1 and λmes2, the temperature dependency of the wavelength at thebias current Imes is linearly interpolated, whereby making it possibleto calculate the wavelength λmes=(Imes, Tmes) at Imes and Tmes.

In addition, although the bias current dependency of wavelengths islinearly interpolated in the above method, another wavelengthcalculating method, in which the bias current dependency is approximatedby such as a quadratic function in order to improve the calculationaccuracy of wavelengths, may be employed. In detail, six wavelengths arefirst extracted from the storage portion 2. Four wavelengths (λ11=λ(I1,T1), λ21=λ(I2, T1), λ12=λ(I1, T2), and λ22=λ(I2, T2)) are extracted asin the above-described method. By selecting the bias current I3differing from the bias currents I1 and I2, the remaining twowavelengths (λ31=λ(I3, T1) and λ32=λ(I3, T2)) are extracted. Next, thebias current dependency of wavelengths at temperature T1 is approximatedby a quadratic function using λ11, λ21 and λ31. The bias currentdependency of wavelengths at temperature T2 is approximated by aquadratic function using λ12, λ22 and λ32. It is thereby possible tocalculate wavelength λmes=(Imes, Tmes) at Imes and Tmes.

Still another wavelength calculating method may be employed. Forexample, it is possible to calculate wavelengths by using matricesindicating the relationship between the laser diode temperature andwavelengths stored in the storage portion 2, or the relationship betweenthe laser diode temperature, bias current and wavelengths. In this mode,the wavelengths are extracted by causing the measured value oftemperature and measured value of the bias current to correspond toeither one of the stored value of the temperature or stored values ofthe temperature and the bias current in the matrices.

Next, a description is given of a wavelength monitoring and controllingmethod in an optical transmitter module or an optical transmitter andreceiver module according to a third embodiment.

FIG. 8 is a flow chart showing a procedure to describe the wavelengthmonitoring and controlling method in an optical transmitter module oroptical transmitter and receiver module according to the thirdembodiment. In detail, in the case of SFP, it is necessary to add atemperature adjusting portion.

First, the temperature, bias current and optical output are measured bythe measurement portion 1 (S11). Next, by mapping (S12) in the Real TimeDiagnostic Interface of the storage portion 2, the optical output iscompared with the minimum threshold value of the optical output warningin the Alarm and Warning Thresholds of the storage portion 2 (S13). Whenthe optical output is smaller than or equal to the minimum thresholdvalue of the optical output warning, the Output Power LOW warning bit inthe Real Time Diagnostic Interface of the storage portion 2 is set to 1(S15). The information is transmitted to the LD drive currentcontrolling circuit 7 to raise the bias current (S17). After the processis over, the temperature, bias current and optical output are againmeasured by the measurement portion 1.

When the optical output is larger than or equal to the minimum thresholdvalue of the optical output warning, next, it is compared with themaximum threshold value of the optical output warning in the Alarm andWarning Thresholds of the storage portion 2 (S14). If the optical outputis larger than or equal to the maximum threshold value of the opticaloutput warning, the Output Power HIGH warning bit in the Real TimeDiagnostic Interface of the storage portion 2 is set to 1 (S16). Theinformation is transmitted to the LD drive current controlling circuit 7to lower the bias current (S18). After the process is over, thetemperature, bias current and optical output are again measured by themeasurement portion 1.

The optical output control is carried out by the central controllingportion 3. Also, the increment step of the LD drive current controllingcircuit 7 is set in accordance with required accuracy. And, if theoptical output is smaller than or equal to the maximum threshold valueof an optical output warning, a status is set, in which the opticaloutput warning signal in the Real Time Diagnostic Interface of thestorage portion 2 is not outputted (that is, the warning bit is set to0), and the wavelength is calculated by collating only the temperatureinformation or temperature and bias current information with thematrices in the User Writable EEPROM or the extended memory portion(S19).

Next, the minimum threshold value of wavelength warning in the Alarm andWarning Thresholds of the storage portion 2 is compared with thetransmitted wavelength information (S20). When the wavelengthinformation is smaller than or equal to the minimum threshold value ofwavelength warning, the Wavelength LOW warning bit in the Real TimeDiagnostic Interface of the storage portion 2 is set to 1 (S22). Theinformation is transmitted to the temperature adjusting portion 9, andthe internal temperature is raised by the temperature adjusting portion9 (S24). After the process is over, the temperature, bias current andoptical output are again measured by the measurement portion 1.

When the wavelength information is larger than or equal to the minimumthreshold value of wavelength warning, next, it is compared with themaximum threshold value of wavelength warning in the Alarm and WarningThresholds of the storage portion 2. When the wavelength information islarger than or equal to the maximum threshold value of wavelengthwarning, the Wavelength HIGH warning bit in the Real Time DiagnosticInterface of the storage portion 2 is set to 1 (S23). If the WavelengthHIGH warning bit in the Real Time Diagnostic Interface of the storageportion 2 is 1, the internal temperature is lowered by the temperatureadjusting portion 9 (S25). After the process is over, the temperature,bias current and optical output are again measured by the measurementportion 1.

If the wavelength information is smaller than or equal to the maximumthreshold value of wavelength warning, a status is set, in which thewavelength warning signal of the Real Time Diagnostic Interface of thestorage portion 2 is not outputted (that is, the warning bit is 0).Again, the temperature, bias current and optical output are measured bythe measurement portion 1.

The above-described wavelength control is carried out by the centralcontrolling portion 3, including control of time constants, from varyingthe bias current or varying the temperature by the temperature adjustingportion 9 until each of the values to be settled. The increment step ofthe temperature adjusting portion 9 is set in accordance with requiredaccuracy.

FIG. 9 is a flow chart for further simplifying a procedure of thewavelength monitoring and controlling method in an optical transmittermodule or an optical transmitter and receiver module according to athird aspect of the invention. Determination (S13 through S18) withrespect to the threshold values of the optical output may be omittedfrom the procedure of the wavelength monitoring and controlling methodshown in FIG. 8.

FIG. 10 is a flow chart showing another procedure of the wavelengthmonitoring and controlling method in an optical transmitter module oroptical transmitter and receiver module according to the third aspect ofthe invention. A description is given below of the procedure shown inFIG. 10 while comparing it with the procedure shown in FIG. 8.

In the procedure shown in FIG. 8, the wavelength control (S20 throughS25) determines whether the calculated wavelength is within or outsidethe range of the threshold values. If outside the threshold values, thealarm bit is set to 1, and the control information showing whether thetemperature is raised or lowered is fed back to the temperatureadjusting portion. In the procedure of the wavelength monitoring andcontrolling method shown in FIG. 10, a temperature to obtain aprescribed wavelength is calculated and is fed back to the temperatureadjusting portion, whereby it becomes possible to control the wavelengthin a highly stabilized state.

In detail, by collating only the measured temperature information or thetemperature and bias current information with the matrices in the UserWritable EEPROM or the extended memory portion, coefficients of theequation (1) or (2) are obtained, from which the wavelength iscalculated. Next, in the measured bias current, the temperature value togive a prescribed wavelength is calculated from the equation (1) or (2),information is fed back by the temperature adjusting portion so that thecalculated temperature value is obtained (S26). Thereby, the wavelengthis fixed to a prescribed value.

FIG. 11 is a flow chart showing another procedure of the wavelengthmonitoring and controlling method in an optical transmitter module oroptical transmitter and receiver module according to the third aspect ofthe invention. The procedure differs from the procedure shown in FIG. 8in terms of the wavelength monitoring and controlling procedure.

In the procedure shown in FIG. 8, the wavelength control (S20 throughS25) determines whether the calculated wavelength is within or outsidethe range of the threshold values, and the alarm bit is set to 1 onlywhen the wavelength is outside the range, feeding back whether thetemperature is raised or lowered by the temperature adjusting portion.In the wavelength monitoring and controlling procedure shown in FIG. 11,by feeding the control information to obtain a prescribed wavelengthback to the temperature adjusting portion, the wavelength is controlledin a highly stabilized state. As described above, two temperatures, oneof which is a smaller value than the measured temperature and the otherof which is a larger value than the measured temperature, and two biascurrents, one of which is a smaller value than the measured bias currentand the other of which is larger than the measured bias current, areselected from the matrices of the User Writable EEPROM as shown in FIG.2A. And, the wavelengths corresponding thereto are extracted at fourpoints to calculate the wavelength (S8). Next, with respect to themeasured bias current, the temperature value which gives a prescribedwavelength is calculated from the temperature dependency of thewavelength at the bias current Imes, and the information is fed back bythe temperature adjusting portion so that the temperature becomes thecalculated temperature value (S27), whereby the wavelength can be fixedto a prescribed value.

Herein, although the bias current dependency of the wavelength islinearly interpolated, as described above, it may be approximated by aquadratic function, etc., and the calculation accuracy of the wavelengthcan be improved. Further, by sufficiently increasing the number ofelements of matrices (that is, number of data points) and always makingthe wavelength for the measured temperature and bias current coincidentwith one of the data points in the matrices, the calculation procedurebased on linear interpolation may be omitted.

Also, herein, although the optical output and wavelength are adjusted byusing the warning signal as a trigger, another given alarm signal may beused for adjustment as a trigger.

In addition, a feedback method described in the embodiment of thewavelength monitoring and controlling method in an optical transmittermodule or an optical transmitter and receiver module according to thethird aspect of the invention is not limited by whether or not there isa warning bit. Also, the wavelength monitoring and controlling method ofan optical module according to the invention is not limited by the SFP.The method is applicable to all the optical modules comprising: ameasurement portion for measuring the temperature and bias current oronly the temperature in an optical transmitter module or an opticaltransmitter and receiver module; a storage portion in which therelationship between the LD temperature, bias current and wavelengths,or between the LD temperature and wavelengths is stored; and atemperature adjusting portion composed of a central controlling portionfor controlling these components and a temperature controlling device.

Since the wavelength monitoring and controlling method stores, notfluctuation deviations from a prescribed wavelength, but the wavelengthsthemselves in its memory, it is possible to set a wavelength emittedfrom the LD to an any value in the temperature-variable range of thetemperature adjusting portion, and the method may be used for awavelength-varying light source.

1. An optical module being an optical transmitter module or opticaltransmitter and receiver module internally comprising: a measurementportion for measuring a laser diode temperature and bias current or onlythe temperature; a storage portion in which the relationship between thetemperature, bias current and wavelengths or between the temperature andwavelengths is stored; and a central controlling portion for controllingthe measurement portion and the storage portion; wherein a wavelength iscalculated on the basis of the relationship stored in the storageportion.
 2. The optical module according to claim 1 comprising a laserdiode drive current controlling circuit provided therein, which controlsthe drive current of the laser diode, and includes a feature of feedingthe bias current information calculated from the measurement portionback to the laser diode drive current controlling circuit.
 3. Theoptical module according to claim 1 or 2 comprising a temperatureadjusting portion composed of a temperature controlling device providedtherein and includes a feature of feeding the wavelength informationcalculated from the storage portion back to the temperature adjustingportion.
 4. A method for monitoring wavelengths in an opticaltransmitter module or optical transmitter and receiver module internallyincluding a measurement portion for measuring a laser diode temperatureand bias current or only the temperature, a storage portion in which therelationship between the temperature, bias current and wavelengths orbetween the temperature and wavelengths is stored, and a centralcontrolling portion for controlling the measurement portion and thestorage portion, wherein the method comprising a step of: calculatingwavelength information on the basis of the temperature and bias currentor the temperature measured by the measurement portion, and therelationship between the laser diode temperature and wavelengths orbetween the laser diode temperature, bias current and wavelengths storedin the storage portion.
 5. The method for monitoring wavelengthsaccording to claim 4, wherein the step for calculating wavelengthinformation obtains λc, ic, a, and b in Equation (1) or λc and a inEquation (2) by using the temperature and bias current or thetemperature measured by the measurement portion, and the relationshipbetween the laser diode temperature and wavelengths or between the laserdiode temperature, bias current and wavelengths stored in the storageportion, and calculates wavelength information;λ=λc+aT+b(i−ic)   Equation (1)λ=λc+aT   Equation (2) (where λc is a wavelength at temperature 0° C.and threshold current value ic, a and b are coefficients, T is atemperature, and i is a bias current).
 6. The method for monitoringwavelengths according to claim 4, wherein the step of calculatingwavelength information selects a smaller temperature value T1 than themeasured temperature Tmes, a larger temperature value T2 than themeasured temperature Tmes, a smaller bias current value I1 than themeasured bias current Imes and a larger bias current value I2 than thebias current value Imes by using the temperature and bias currentmeasured by the measurement portion, and the relationship between thelaser diode temperature, bias current and wavelengths stored in thestorage portion; extracts four wavelengths (λ11=λ(I1, T1), λ21=λ(I2,T1), λ12=λ(I1, T2), and λ22=λ(I2, T2)) corresponding thereto; andcalculates the wavelength λmes1=λ(Imes, T1) at the measured bias currentImes by linearly interpolating the bias current dependency of thewavelengths at temperature T1 using λ11 and λ21; calculates thewavelength λmes2=(Imes, T2) at the measured bias current Imes bylinearly interpolating the bias current dependency of the wavelength attemperature T2 using λ12 and λ22; and calculates the wavelengthλmes=(Imes, Tmes) at the measured bias current Imes and temperature Tmesby linearly interpolating the temperature dependency of the wavelengthat the bias current Imes using the calculated λmes1 and λmes2.
 7. Themethod for monitoring wavelengths according to claim 4, wherein the stepof calculating wavelength information selects a smaller temperature T1than the measured temperature Tmes, a larger temperature T2 than themeasured temperature Tmes, a smaller bias current I1 than the measuredbias current Imes, a larger bias current I2 than the measured biascurrent Imes, and a bias current I3 differing from the bias currents I1and I2 by using the temperature and bias current measured by themeasurement portion, and the relationship between the laser diodetemperature, bias current and wavelengths stored in the storage portion;extracts six wavelengths (λ11=λ(I1, T1), λ21=λ(I2, T1), λ12=λ(I1, T2),λ22=λ(I2, T2), λ31=λ(I3, T1), and λ32=λ(I3, T2) corresponding thereto;approximates the bias current dependency of the wavelength at thetemperature T1 by a quadratic function using λ11, λ21 and λ31;approximates the bias current dependency of the wavelength at thetemperature T2 by a quadratic function using λ12, λ22 and λ32; andcalculates the wavelength λmes=λ(Imes, Tmes) at the measured biascurrent Imes and temperature Tmes.
 8. The method for monitoringwavelengths according to claim 4, wherein the step of calculatingwavelength information extracts a wavelength information by causing themeasured temperature and bias current to correspond to any one of thetemperatures or the temperature and bias current stored in matricesindicating the relationship between the laser diode temperature andwavelengths or between the laser diode temperature, bias current andwavelength stored in the storage portion.
 9. A method for monitoring andcontrolling wavelengths of an optical transmitter module or opticaltransmitter and receiver module internally including: a measurementportion for measuring a laser diode temperature and bias current or onlythe temperature; a storage portion in which the relationship between thetemperature, bias current and wavelengths or between the temperature andwavelengths is stored; a central controlling portion for controlling themeasurement portion and the storage portion; and a temperature adjustingportion composed of a temperature controlling device, wherein the methodcomprising steps of: calculating wavelength information on the basis ofthe temperature and bias current or only the temperature measured by themeasurement portion, and the relationship between the laser diodetemperature and wavelengths or between the laser diode temperature, biascurrent and wavelengths stored in the storage portion; and adjusting andcontrolling the internal temperature by feeding back to the temperatureadjusting portion using the calculated wavelength information.
 10. Themethod for monitoring and controlling wavelengths to claim 9, furthercomprising a step of: comparing the threshold values, in which theminimum value and maximum value of wavelengths are predetermined, withthe wavelength information calculated in the step of calculatingwavelength information; wherein the step for controlling temperaturefeeds back to the temperature adjusting portion when the result ofcomparison made by the wavelength information comparing step is outsidethe threshold values, lowering the internal temperature by thetemperature adjusting portion when the result is smaller than or equalto the minimum value of the threshold values, and raising the internaltemperature by the temperature adjusting portion when the result islarger than or equal to the maximum value of the threshold values. 11.The method for monitoring and controlling wavelengths according to claim10, wherein, the step of calculating wavelength information uses thetemperature and bias current or only the temperature measured by themeasuring portion, and the relationship between the laser diodetemperature and wavelengths or between the laser diode temperature, biascurrent and wavelengths stored in the storage portion, and calculateswavelength information by obtaining λc, ic, a, and b in Equation (1) orλc and a in Equation (2);λ=λc+aT+b(i−ic)   Equation (1)λ=λc+aT   Equation (2) (where λc is a wavelength at temperature 0° C.and threshold current value ic, a and b are coefficients, T is atemperature, and i is a bias current).
 12. The method for monitoring andcontrolling wavelengths according to claim 10, wherein the step ofcalculating wavelength information selects a smaller temperature valueT1 than the measured temperature Tmes, a larger temperature value T2than the measured temperature Tmes, a smaller bias current value I1 thanthe measured bias current Imes and a larger bias current value I2 thanthe bias current value Imes by using the temperature and bias currentmeasured by the measurement portion, and the relationship between thelaser diode temperature, bias current and wavelengths stored in thestorage portion; extracts four wavelengths (λ11=λ(I1, T1), λ21=λ(I2,T1), λ12=λ(I1, T2)), and λ22=λ(I2, T2) corresponding thereto; andcalculates the wavelength λmes1=λ(Imes, T1) at the measured bias currentImes by linearly interpolating the bias current dependency of thewavelengths at temperature T1 using λ11 and λ21; calculates thewavelength λmes2=(Imes, T2) at the measured bias current Imes bylinearly interpolating the bias current dependency of the wavelength attemperature T2 using λ12 and λ22; and calculates the wavelengthλmes=(Imes, Tmes) at the measured bias current Imes and temperature Tmesby linearly interpolating the temperature dependency of the wavelengthat the measured bias current Imes using the calculated λmes1 and λmes2.13. The method for monitoring and controlling wavelengths according toclaim 10, wherein the step of calculating wavelength information selectsa smaller temperature T1 than the measured temperature Tmes, a largertemperature T2 than the measured temperature Tmes, a smaller biascurrent I1 than the measured bias current Imes, a larger bias current I2than the measured bias current Imes, and a bias current I3 differingfrom the bias currents I1 and I2 by using the temperature and biascurrent measured by the measurement portion and the relationship betweenthe laser diode temperature, bias current and wavelengths stored in thestorage portion; extracts six wavelengths (λ11=λ(I1, T1), λ21=λ(I2, T1),λ12=λ(I1, T2), λ22=λ(I2, T2), λ31=λ(I3, T1)), and λ32=λ(I3, T2)corresponding thereto; approximates the bias current dependency of thewavelength at the temperature T1 by a quadratic function using λ11, λ21and λ31; approximates the bias current dependency of the wavelength atthe temperature T2 by a quadratic function using λ12, λ22 and λ32; andcalculates the wavelength λmes=λ(Imes, Tmes) at the measured biascurrent Imes and temperature Tmes.
 14. The method for monitoring andcontrolling wavelengths according to claim 10, wherein the step ofcalculating wavelength information extracts a wavelength by causing themeasured temperature and bias current to correspond to any one of thetemperatures stored in matrices indicating the relationship between thelaser diode temperature and wavelengths or between the laser diodetemperature, bias current and wavelengths stored in the storage portion.15. The method for monitoring and controlling wavelengths according toclaim 9, wherein the step of calculating wavelength information obtainsλc, ic, a, and b in Equation (1) or λc and a in Equation (2) by usingthe temperature and bias current or only the temperature measured by themeasuring portion, and the relationship between the laser diodetemperature and wavelengths or between the laser diode temperature, biascurrent and wavelengths stored in the storage portion, and calculateswavelength information; and the step of controlling temperaturecalculates a temperature, which gives a prescribed wavelength by usingthe calculated wavelength information and Equations (1) or (2), andfeeds it back to the temperature adjusting portion so as to secure saidtemperature;λ=λc+aT+b(i−ic)   Equation (1)λ=λc+aT   Equation (2) (where λc is a wavelength at temperature 0° C.and threshold current value ic, a and b are coefficients, T is atemperature, and i is a bias current).
 16. The method for monitoring andcontrolling wavelengths according to claim 9, wherein the step ofcalculating wavelength information selects a smaller temperature valueT1 than the measured temperature Tmes, a larger temperature value T2than the measured temperature Tmes, a smaller bias current value I1 thanthe measured bias current Imes and a larger bias current value I2 thanthe bias current value Imes by using the temperature and bias currentmeasured by the measurement portion, and the relationship between thelaser diode temperature and bias current and wavelengths stored in thestorage portion; extracts four wavelengths (λ11=λ(I1, T)1, λ21=λ(I2,T1), λ12=λ(I1, T2), and λ22=λ(I2, T2) corresponding thereto; andcalculates the wavelength λmes1=λ(Imes, T1) at the measured bias currentImes by linearly interpolating the bias current dependency of thewavelengths at temperature T1 using λ11 and λ21; calculates thewavelength λmes2=(Imes, T2) at the measured bias current Imes bylinearly interpolating the bias current dependency of the wavelength attemperature T2 using λ12 and λ22; and calculates the wavelengthλmes=(Imes, Tmes) at the measured bias current Imes and temperature Tmesby linearly interpolating the temperature dependency of the wavelengthat the measured bias current Imes using the calculated wavelength λmes1and λmes2; and the step for controlling temperature calculates atemperature, which gives a prescribed wavelength at the measured biascurrent Imes, on the basis of the temperature dependency of thewavelength, and feeds it back to the temperature adjusting portion so asto secure the calculated temperature.
 17. The method for monitoring andcontrolling wavelengths according to claim 9, wherein the step ofcalculating wavelength information selects a smaller temperature T1 thanthe measured temperature Tmes, a larger temperature T2 than the measuredtemperature Tmes, a smaller bias current I1 than the measured biascurrent Imes, a larger bias current I2 than the measured bias currentImes, and a bias current I3 differing from the bias currents I1 and I2by using the temperature and bias current measured by the measurementportion, and the relationship between the laser diode temperature, biascurrent and wavelengths stored in the storage portion; extracts sixwavelengths (λ11=λ(I1, T1), λ21=λ(I2, T1), λ12=λ(I1, T2), λ22=λ(I2, T2),λ31=λ(I3, T1), and λ32=λ(I3, T2) corresponding thereto; approximates thebias current dependency of the wavelength at the temperature T1 by aquadratic function using λ11, λ21 and λ31; approximates the bias currentdependency of the wavelength at the temperature T2 by a quadraticfunction using λ12, λ22 and λ32; and calculates the wavelengthλmes=λ(Imes, Tmes) at the measured bias current Imes and temperatureTmes; and the step for controlling temperature calculates a temperature,which gives a prescribed wavelength at the measured bias current Imes,on the basis of the temperature dependency of the wavelength, and feedsit back to the temperature adjusting portion so as to secure thecalculated temperature.
 18. The method for monitoring and controllingwavelengths according to claim 9, wherein the step of calculatingwavelength information extracts a wavelength information by causing themeasured temperature and bias current to correspond to any one of thetemperatures stored in matrices indicating the relationship between thelaser diode temperature and wavelengths or between the laser diodetemperature, bias current and wavelengths stored in the storage portion;and the step of controlling temperature extracts a temperature from thematrices, which gives a prescribed wavelength at the corresponding biascurrent, and feeds it back to the temperature adjusting portion so as tosecure the extracted temperature.
 19. A method for monitoring andcontrolling wavelengths according to any one of claims 9 through 18,further comprising a laser diode drive current controlling circuit whichcontrols the drive current of the laser diode, wherein, the methodfurther comprising, before the step of calculating wavelengthinformation, steps of: comparing threshold values of an optical outputalarm or warning, in which the minimum value and maximum value ofoptical output are predetermined, with the optical output measured bythe measurement portion; and on the basis of a comparison made by theoptical output comparing step, feeding the result back to the laserdiode drive current controlling circuit when the result is outside therange of the threshold values, raising the bias current by the laserdiode drive current controlling circuit if the result is smaller than orequal to the minimum value of the threshold values, and lowering thebias current by the laser diode drive current controlling circuit if theresult is larger than or equal to the maximum value of the thresholdvalues.